1. Field of the Invention
The present general inventive concept relates to a digital broadcasting receiver and a channel searching method thereof. More particularly, the present general inventive concept relates to a digital broadcasting receiver and a channel searching method of speedily searching channels by searching and storing a digital signal and an analog signal in parallel.
2. Description of the Related Art
As digital technique has been developed, a broadcasting system initially transmitted using an analog signal, such as a NTSC, PAL or SECAM system, can be transmitted by a digital system, such as ATSC, DVB-T, ISDB-T or QAM, and it has been commercially available to transmit a digital broadcasting signal using a satellite. However, digital broadcasting equipment and digital broadcasting receivers are relatively expensive, and digital broadcasting technique is yet to be completed. As such, an analog system and a digital system are both used for a certain transition period until the digital broadcasting technique is completely systemized and the digital broadcasting receiver becomes widely distributed to users.
In order to realize both the analog system and the digital system, a broadcasting receiver is required to receive both an analog broadcasting signal and a digital broadcasting signal, and in order to meet this requirement, a combination digital broadcasting receiver has been developed, which has a tuner capable of receiving both the analog broadcasting signal and the digital broadcasting signal.
One of characteristics of a digital broadcast and digital broadcasting receiver is multi-channelization. If an analog broadcasting system is applied, only one program can be transmitted through a single bandwidth. However, if a digital broadcasting system is applied, four programs can be transmitted through a single bandwidth because the digital broadcasting system applies MPEG2 technique which can compress and restore an image and a sound in a high density to simultaneously transmit the four programs. Due to multi-channelization of digital broadcasting, a user can select various broadcasting signals of a clear image quality.
A user selects a desirable channel using a remote controller or channel selection means attached to a main body. Since there are a variety of digital broadcasting channels, a digital broadcasting receiver generally has a function of automatic channel search (ACS) for automatically setting a channel without requiring a user's selection. The ACS function is an automatic channel search function, which skips channels that are not capable of receiving a broadcasting signal or channels that have a weak signal, to automatically set the channel capable of receiving the broadcasting signal.
FIG. 1 is a block diagram explaining a general combination digital broadcasting receiver having an ACS function. Referring to FIG. 1, the combination digital broadcasting receiver receives both analog and digital broadcasting signals and comprises a RF switch 10, an analog tuner part 21, a digital tuner part 23, an analog signal demodulation part 30, a digital signal demodulation part 40, a CPU 50 and a memory 60.
If the CPU 50 enters an automatic channel searching mode by an external signal, the RF switch 10 distributes the received air or cable analog broadcasting signal and transmits a first analog signal to the analog tuner part 21. The analog tuner part 21 receives a broadcasting signal while tuning from a lowest channel to a highest channel of an analog signal bandwidth, and the tuned analog signal is demodulated by the analog signal demodulation part 30 and transmitted to the CPU 50 in a CVBS signal. The CPU 50 determines a valid channel based on a magnitude of the tuned signal to store in the memory 60.
If the above analog signal channel search is finished, the RF switch 10 transmits the digital broadcasting signal to the digital tuner part 23. The digital tuner part 23 receives the broadcasting signal while tuning from the lowest channel to the highest channel, and the tuned digital signal is transmitted to the digital broadcasting demodulation part 40.
The digital signal demodulation part 40 comprises a plurality of demodulation parts 41 and 43 depending on a digital broadcasting system. In specific, the digital signal demodulation part 40 comprises a quadrature amplitude modulation (QAM) block 41 and a DTV demodulation part 43 to receive the tuned digital signal transmitted in an ATSC (Advanced Television Systems Committee) standard system which is referred to as a USA system, a DVB (Digital Video Broadcasting Terrestrial) standard system which is referred to as a European system, and an ISDM-T (Integrated Services Digital Broadcasting-Terrestrial) standard system which is referred to as a Japanese system.
With respect to a digital signal stream demodulated by the digital signal demodulation part 40, the CPU 50 determines a valid channel to store in the memory 60, thereby finishing the automatic channel search (ACS) for the analog signal and the digital signal.
Digital transmission systems are a very diverse and separate demuxing process, and require video/audio decoding after tuning, and therefore, much time is wasted for converting channels. In addition, the number of digital cable channels is far greater than analog cable channels, for example, there are appropriately five hundred (500) digital cable channels including virtual channels.
If an analog signal channel is first searched and then digital signal channel is searched as a conventional way, it spends much time to search a digital signal channel such that it is inconvenient to user. Even if analog and digital signals are each searched at the same time, it takes much more time to search the digital signal channel. Accordingly, a channel search time is not remarkably reduced.